[PATCH] tile: ns2cycles should use __raw_get_cpu_var

From: Henrik Austad
Date: Sat Mar 23 2013 - 03:35:17 EST

ns2cycles use per_cpu variables, and will, eventually, find its way into
smp_processord_id(). This is not safe in a preemptible kernel,
preemption should ideally be disabled.

BUG: using smp_processor_id() in preemptible [00000000] code:
caller is ns2cycles+0x40/0xb8

Starting stack dump of tid 367, pid 367 (systemd-modules) on cpu 2 at
cycle 20969956421
frame 0: 0xfffffff70004b860 dump_stack+0x0/0x20 (sp 0xfffffe407993fa90)
frame 1: 0xfffffff7006abc28 debug_smp_processor_id+0x1a8/0x1e0 (sp
frame 2: 0xfffffff7004d7b40 ns2cycles+0x40/0xb8 (sp 0xfffffe407993fab8)
frame 3: 0xfffffff7004dc578 __ndelay+0x38/0x80 (sp 0xfffffe407993fae0)

However, in this case:

- the frequency is the same accross all cores
- we use the data read-only
- we do not scale the frequency

Which means that we can use the __raw_get_cpu_var instead.

Signed-off-by: Henrik Austad <haustad@xxxxxxxxx>
arch/tile/kernel/time.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c
index 42297f6..4e87cb9 100644
--- a/arch/tile/kernel/time.c
+++ b/arch/tile/kernel/time.c
@@ -234,7 +234,9 @@ int setup_profiling_timer(unsigned int multiplier)
cycles_t ns2cycles(unsigned long nsecs)
- struct clock_event_device *dev = &__get_cpu_var(tile_timer);
+ /* we don't have to disable preemptions here as each core has the same
+ * clock-frequency */
+ struct clock_event_device *dev = &__raw_get_cpu_var(tile_timer);
return ((u64)nsecs * dev->mult) >> dev->shift;


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